A train moves 120 km at 60 km/h and then another 60 km at 30 km/h. What is the average speed for the entire journey?

To find the average speed for the entire journey, we use the basic formula for average speed:

$\text{Average Speed}=\frac{\text{Total Distance}}{\text{Total Time}}$

Let's break down the journey into two parts:

Part 1:
The train moves a distance of 120 km at a speed of 60 km/h.
We can calculate the time taken ($$_t1) for this part of the journey using the formula $\text{Time}=\frac{\text{Distance}}{\text{Speed}}$:
$$_t1=12060=2 hours

Part 2:
The train moves another distance of 60 km at a speed of 30 km/h.
We calculate the time taken ($$_t2) for this second part:
$$_t2=6030=2 hours

Total Journey Calculations:
Now, we find the total distance and total time for the entire trip:
$\text{Total Distance}=120\text{km}+60\text{km}=180\text{km}$
$\text{Total Time}=2\text{hours}+2\text{hours}=4\text{hours}$

Finally, we calculate the average speed:
$\text{Average Speed}=\frac{180}{4}=45\text{km/h}$

Therefore, the average speed for the entire journey is 45 km/h.